By using the difference in the volatility of the components in the liquid mixture, the liquid mixture is partially vaporized and the vapor is partially condensed, so as to achieve the separation of the components it contains. It is a unit operation that belongs to mass transfer separation. Widely used in oil refining, chemical, light industry and other fields.
The principle is based on the separation of a two-component mixture. The material liquid is heated to make it partially vaporized, and the volatile components are concentrated in the vapor, and the non-volatile components are also concentrated in the remaining liquid, which achieves the separation of the two components to a certain extent. The greater the difference in volatility of the two components, the greater the degree of enrichment described above. In industrial distillation equipment, a partially vaporized liquid phase is brought into direct contact with a partially condensed gas phase for vapor-liquid interstitial mass transfer. As a result, the non-volatile components in the gas phase are partially transferred to the liquid phase, and The volatile components are partially transferred to the gas phase, that is, partial vaporization of the liquid phase and partial condensation of the vapor phase are achieved at the same time.
Distillation principle and operation process
Simple distillation is a batch operation process. The feed liquid is added to a distillation kettle, and the liquid is heated and boiled under constant pressure to continuously vaporize the liquid. The steam generated one after the other is cold-leached and used as the top product, where the volatile components are relatively enriched. During the distillation process, the volatile matter concentration of the liquid in the kettle continuously decreased, and the volatile matter concentration in the steam also decreased accordingly.
To achieve high-purity separation, rectification can be used. Distillation is the most commonly used distillation method. One part is returned to the top of the column, which is called reflux liquid, and the rest is continuously discharged as the top product (distillate). In the upper part of the tower (above the feeding position), the countercurrent contact and the material and energy transfer are performed between the rising steam and the reflux liquid. The bottom of the column is equipped with a reboiler (distillation kettle) to heat the liquid to produce steam. The steam rises along the tower, contacts the falling liquid countercurrently and conducts material energy transfer, and the bottom of the tower continuously discharges part of the liquid as the bottom product. The rising steam is partially condensed many times, and the temperature gradually decreases. The concentration of volatile component A gradually increases. The falling liquid is partially gasified many times. The temperature gradually increases, and the concentration of non-volatile component B gradually increases. The concentration gradually decreases, the temperature distribution in the tower gradually decreases from the bottom to the top, and the concentration of the A component gradually increases from the bottom to the top. In the rectification section, the lower part of the column has completed the concentration of the heavy components in the descending liquid, that is, the light component is proposed, so it is called the stripping section. In such a column, a two-component mixture can be continuously separated High purity light and heavy two components. It can be seen that the difference between rectification and distillation lies in 'reflux.' Reflux is a necessary condition for gas and liquid contact mass transfer.
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